title: Imaging the intact mouse cornea using coherent anti-stokes Raman scattering (CARS).
abstract: OBJECTIVE
  The aim of this study was to image the cellular and noncellular structures of the cornea and limbus in an intact mouse eye using the vibrational oscillation of the carbon-hydrogen bond in lipid membranes and autofluorescence as label-free contrast agents.
  
  
  METHODS
  Freshly enucleated mouse eyes were imaged using two nonlinear optical techniques: coherent anti-Stokes Raman scattering (CARS) and two-photon autofluorescence (TPAF). Sequential images were collected through the full thickness of the cornea and limbal regions. Line scans along the transverse/sagittal axes were also performed.
  
  
  RESULTS
  Analysis of multiple CARS/TPAF images revealed that corneal epithelial and endothelial cells could be identified by the lipid-rich plasma membrane CARS signal. The fluorescent signal from the collagen fibers of the corneal stroma was evident in the TPAF channel. The transition from the cornea to sclera at the limbus was marked by a change in collagen pattern (TPAF channel) and thickness of surface cells (CARS channel). Regions within the corneal stroma that lack collagen autofluorescence coincided with CARS signal, indicating the presence of stromal fibroblasts or nerve fibers.
  
  
  CONCLUSIONS
  The CARS technique was successful in imaging cells in the intact mouse eye, both at the surface and within corneal tissue. Multiphoton images were comparable to histologic sections. The methods described here represent a new avenue for molecular specific imaging of the mouse eye. The lack of need for tissue fixation is unique compared with traditional histology imaging techniques.
authors.affiliation: Department of Ophthalmology, University of Colorado Denver, Aurora, Colorado 80045, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Ammar
authors.forename: Tim C
authors.initials: TC
authors.lastname: Lei
authors.forename: Malik Y
authors.initials: MY
authors.lastname: Kahook
authors.forename: Omid
authors.initials: O
authors.lastname: Masihzadeh
mesh_terms: D000818:Animals; D003094:Collagen / Q000032:analysis*; D003315:Cornea / Q000737:chemistry* / Q000166:cytology; D003319:Corneal Stroma / Q000737:chemistry / Q000166:cytology; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D016850:Limbus Corneae / Q000737:chemistry / Q000166:cytology; D051379:Mice; D008807:Mice, Inbred BALB C; D036641:Microscopy, Fluorescence, Multiphoton; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D003094:Collagen
keywords: coherent anti-Stokes Raman scattering (CARS); cornea; corneal stroma